The unusual combination of anisotropic and fluid behavior of liquid crystals has resulted in their use in a multiplicity of electro-optic switching and indicating devices. In this connection, use may be made of their electrical, magnetic, elastic and/or thermal properties to produce changes in orientation. Optical effects can then be achieved, for example, with the aid of birefrigence, of the incorporation of dichroically absorbing dyestuff molecules ("guest-host mode") or of light scattering.
To fulfill the continuously increasing practical requirements in the various fields of application, there is a constant need for novel improved liquid-crystal ("Liquid-Crystal") mixtures and consequently, also for a multiplicity of mesogenic compounds having a wide variety of structures. This is the case both for those fields in which nematic LC phases (for example TN="twisted nematic", STN="supertwisted nematic", SBE-"supertwisted birefringence effect", ECB="electrically controlled birefrigence") are used and also for those involving smectic LC phases (for example, ferroelectric, electroclinic).
Many of the compounds which are suitable for LC mixtures can be described by a construction principle (building system) (see, for example, J. Am. Chem. Soc. 108, 4736 (1986), structure I; Science 231, 350 (1986), FIG. 1A; J. Am. Chem. Soc. 108, 5210 (1986), FIG. 3), in which nuclei of cyclic compounds--aromatics, heteroaromatics, but also saturated ring systems--are linked to straight--chain alkyl side chains or alkyl side chains which are substituted in the chain by small groups (for example methyl, chlorine) and are consequently branched. Compounds which have a terminal silyl-substituted alkyl chain as a substructure are known, for example, from EP-A-0,136,501, DE-A-3,521,201 and 3,601,742. In these molecules, the Si atom has readily hydrolyzable substituents which are said to enable these compounds, in particular, to produce a homeotropic orientation of the liquid-crystalline phases on the surface. A liquid-crystalline behavior of the compounds is not reported, only their use as components of liquid-crystalline dielectrics.